There are many different schools of thought on early childhood education. Some people want to start kids with formal learning as soon as possible and others prefer to wait until later. (I lean more toward the latter.) Some people want to have everything laid out for them with a schedule and others want to do their own thing when it's best for them. (Do you even have to ask which one I am?) And of course there are parents who are looking for educational things to do with their kids until they reach school age and those who are planning to homeschool. All of that to say that your situation will have a big influence on what you are looking for.
You know what I think is the most helpful tip in homeschooling? Be organized. Yes, readers, this is the point where I realize I have lost all the notes I jotted down earlier. Perhaps the back of a wedding invitation envelope was not the best place to empty my mind. You might check back later to see if I've added anything!
What We Did/Are Doing
With Jack, we read, read, read, which is the best thing you can do for your child, educationally speaking, no matter what future schooling plans you have. We went to the library often, usually a couple of times a week since our library was so great. We went to zoo classes and museums. And we read, read, read.
When Jack was 3, I sort-of started "doing school" with him--I don't think that's necessarily something that we needed to do, but when you have one child and you're home with them, you've got to do something to fill your time and it might as well be educational. After all, you can only watch so much Nick Jr. before you want to scream. We were very relaxed about it and worked on letters and numbers and that sort of thing. We also started doing some of the stories from Before Five in a Row, using the lapbook pieces from Homeschool Share. He loved these and will still get these out to look at and reminisce. When he was 4, I had great plans for school every morning and we got off to a great start...until I got pregnant. It went downhill from there and honestly, he still learned a lot, because that's what kids do. We did pick back up and finish strong with some different Five In A Row and unit studies.
Being the second child, Alice does not get to the library or zoo classes or the museum as much as Jack did, but we still read, read, read, and she seems fairly bright, though she will protest if you tell her she is smart. Now that some of her old activities aren't as entertaining, this year we'll probably start with a set time for her to work on things with me in a very relaxed way. I am hoping the focused attention on her before I start with Jack might make it easier for her to move on while we're doing the second grade stuff. Really, though, she's probably going to want to get right in there and do whatever he's doing. It may be a long year!
Here are a few of my favorite resources, along with some rambling commentary!
Making Learning Fun There are so many great learning and craft ideas here to go along with just about any theme you can think of!
PreKinders This is more of a classroom site, but I've found a lot of great ideas and printables here for use at home.
Mailbox Magazine You can probably find most of this stuff for free elsewhere, but I like to get something in my mailbox that I can flip through while the kids are in the tub or I'm stirring dinner (because I'm all old-school and have a phone, not a "mobile device") and there is stuff that I can use immediately. They have lots of different levels and you can get some of their old yearbook compilations for pretty cheap, too!
KidsSoup This is a subscription site I used when Jack was younger. They have even more things now, so I might think about subscribing again later for Alice.
Enchanted Learning This is a great site for older kids, too. There are tons of free items or you can subscribe for access to everything.
Teachers Pay Teachers I found this site this year and purchased several units. The link will take you to a teacher I have found lots of good things from, but you can search the whole site and find lots of freebies, too.
ToddlerToddler Way back before I even thought about homeschooling, I used this site for some fun games and activities for Jack, The shape game is sitting on our table right now!
Real Learning If you're planning on homeschooling, you need this book. I'm not Catholic and I don't have a large family, but I love love love Elizabeth Foss.
Heather's Preschool Post Whatever I've left out of this post, Heather probably has it. (By the way, my laundry game that is linked there can be found here. I just now sent a link to the commenters who asked for that. I'm a little slow sometimes.)
And of course, there are plenty of companies (Abeka, Sonlight, etc.) that will be happy to sell you a complete formal curriculum for your little, but I think your time and money will be better spent on books and play and going outside.
Anything I've left out? If you have any questions, please let me know!